Jim,
You wrote:
I know the answer but still have to log the question...for posterity...doesn't the golf course have to be routed and drawn by the date of that letter if Piper is going to pick the area of soil to analyze to advise on the best short growing grasses?
In this case, you may recall that parts, but not all of the Johnson farm were blessed with a cover of what later became known as Merion Bluegrass. Those lettered areas corresponded to areas of this natural grass for the most part, or lack thereof. So, it is quite possible that the routing had no bearing on the soil and turf tests at all. Many holes, (from memory, 14, 18 and that general area, but I could be wrong) required no planting, just mowing, while other areas would have required perhaps draining, fertilizing, etc. because of varying soils.